1. Field of the Invention
The present invention relates to a muffler structure for damping the exhaust noise from an engine of a vehicle or the like.
2. Description of Background Art
A conventionally known type of muffler has a double-pipe structure, and the type of muffler includes an inner tube and an outer tube (see, for example, Japanese Patent Application Laid-Open No. 2006-070705). An annular step portion is formed in each of the front- and the rear-end portions of the inner tube, while each annular step portion is brought into contact with, all along its circumference, the outer tube from inside. One of the front and the rear step portions is fixed to the outer tube, while the other one of the step portions is allowed to slide relative to the outer tube. With this structure, the muffler can cope with the difference in thermal expansion between the inner tube and the outer tube.
In the above-mentioned muffler structure, the inner tube, which has the front and the rear step portions, is formed to be more rigid than the outer tube. The two tubes are supposed to be brought into close contact with each other. For this purpose, when the inner tube is inserted into the outer tube, the cross-sectional shape of the outer tube is deformed to fit to the cross-sectional shape of the inner tube. In an outer tube with a perfectly circular shape, the cross-sectional shape is hard to deform to expand. While the inner tube and the outer tube are supposed to be brought into close contact with each other, there may sometimes be a gap that are unintentionally created between these two tubes because of the above and other causes. In addition, a difference in thermal expansion between the inner tube and the outer tube may sometimes create a gap, though unintentionally, even between the two tubes both of which are allowed to slide relatively to each other. When such a gap is created, the gap causes abnormal noise to be generated in the muffler.
Under the above circumstances, the present invention provides a muffler structure capable of suppressing the generation of abnormal noise in the muffler even when the outer and the inner tubes expand thermally.